Biomedical subjects
Publications and source records attributed to H E Clark.
This study was undertaken to assess the effect of mixing speed on the setting rate of high-copper dental amalgam. The surface hardness during setting of two representative brands of dental amalgam was related to working and carving times determined by clinicians. From this information, a means of evaluating setting rate of amalgam based on surface hardness was developed.
Explore the source record for details and available documents.
Fluoride release from three commercial glass ionomer filling cements and three glass ionomer luting cements was measured in the laboratory over a 12-month period. Fluoride release from these glass ionomer cements was compared with that released from a silicate, silicophosphate, and a fluoride-containing polycarboxylate cement. The fluoride released from the glass ionomer cements throughout the one-year period was similar, both in quantity and pattern, to that released by the silicate cement. The silicophosphate cement tended to release fluoride in somewhat lesser amounts, while the amount of fluoride released by the polycarboxylate was negligible after the first few days. Analysis of these data indicates that these glass ionomer cements probably possess anticariogenic properties similar to those of silicate cement.
Explore the source record for details and available documents.
The fluoride determinations were done on enamel biopsies taken before and after restoration of extracted teeth with silicate cement. Two sites, one near the restoration and one 3 mm or more away from the restoration, were assayed. No difference was noted in pre- and post-restoration biopsies when teeth were restored with a fluoride-free silicate. Post-restoration biopsies at sites near and away from the restoration were significantly higher in fluoride as compared to pre-restoration biopsies when the teeth were restored with a fluoride-containing silicate.
Nitrogen retention of adults who consumed diets in which cereals furnished 6.0 g N and 0.9 g of lysine was improved by increasing lysine to 1.8 g without altering other amino acids. In a second experiment, 70% of the 6.0 g of dietary N was supplied by rice + wheat and 30% by mixtures of amino acids so designed that the total intakes of amino acids were equivalent to those in diets containing 6.0 g N from whole egg (E), egg + potato (EP), rice + wheat (RW), rice + soy (RS), wheat + milk (WM) or corn + beans (CB). Mean N balances of young men in descending order were, g/day: E 0.69 +/- 0.23, RS 0.44 +/- 0.15, EP 0.43 +/- 0.09, WM 0.24 +/- 0.16, CB 0.16 +/- 0.13 and RW -0.02 +/- 0.10. In the same order, these diet provided, g/day: lysine 2.6, 1.9, 2.3, 1.6, 1.4 and 1.0; S-acids 2.2, 1.7, 1.6, 2.2, 1.9 and 2.3; and tryptophan 0.7, 0.4, 0.6, 0.5, 0.3 and 0.4. N balances resulting from diets E, RS and EP did not differ significantly from each other but E was superior to CB and RW (P less than 0.01). Relative amounts and propertions of the essential amino acids could be varied without altering nitrogen retention until at least one amino acid became limiting. Several patterns of indispensable amino acids therefore may be equally effective in meeting needs of adults, but both amounts and relative proportions should be considered.
Young men consumed a diet that provided 6.0 g of nitrogen, of which rice, wheat, and milk supplied 33, 38, and 29%, respectively, for 28 days following adjustment. This diet contained amounts of essential amino acids that were at least twice the minimal required amounts reported for men. Mean nitrogen balances in four successive 7-day periods were 0.27 +/- 0.13, 0.25 +/- 0.08, 0.10 +/- 0.07 and 0.24 +/- 0.12 g; and the mean for 28 days was 0.22 +/- 0.05 g. Nitrogen retention did not differ significantly between periods. All men who weighed between 65 and 72 kg retained small amounts of nitrogen but one who weighed 78 kg was in slightly negative balance. The mean balances as reported do not provide an allowance for integumental and other losses. The daily protein intake from these sources, equivalent to 0.5 g/kg of body weight, was a critical level slightly lower than the amount appropriate for long-term maintenance of young men weighing 70 kg.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
A basic diet containing rice, wheat, and corn that furnished 6.0 g of nitrogen per day was consumed by health young adults. Two levels of lysine, 900 and 1800 mg, and three of tryptophan, 260, 390, and 520 mg, were tested. Lysine exerted a significant effect (P less than 0.05) on nitrogen retention but tryptophan did not. When consumed in conjunction with at least twice the reported minimal requirements of other essential amino acids, 900 mg of lysine induced mean daily balances of 0.15 +/- 0.18, 0.19 +/- 0.14, and 0.22 +/- 0.21 g, respectively, in response to the three levels of tryptophan; and 1800 mg of lysine caused retentions of 0.75 +/- 0.14, 0.77 +/- 0.21 and 0.71 +/- 0.15 g. These findings are discussed in relation to fulfillment of protein and amino acid requirements of adult human subjects.
Three isogenic lines of corn provided two levels of nitrogen for young men, but the diets were isonitrogenous at 5.5 g. Mean daily nitrogen balances were -0.28 +/- 0.34, +0.31 +/- 0.23 and 0.40 +/- 0.08 g, respectively, when normal, opaque-2 and sugary-2 opaque-2 corn furnished 5.5 g of nitrogen; and -0.07 +/- 0.17, +0.38 +/- 0.21 and -0.04 +/- 0.25 g when corn supplied only 4.4 g of nitrogen. Although these values were not significantly different, both high-lysine varieties tended to be superior to normal corn at 5.5 g of nitrogen and opaque-2 corn caused improvement even at 4.4 g of nitrogen. Lysine and tryptophan were higher and leucine lower in both opaque-2 and sugary-2 opaque-2 than in normal corn. Coefficients of apparent digestibility were between 65.5% and 68.8%.
Nitrogen retention and concentrations of plasma amino acids were compared when young adults consumed isonitrogenous diets containing proteins (3.0 g of N from rice plus 3.0 g of N from milk or 3.0 g of N from rice plus 3.0 g of N from wheat flour) or mixtures of their constituent amino acids. Diets containing proteins induced greater nitrogen retention than did those containing corresponding amounts of amino acids in crystalline form, and the difference between the combinations of proteins was delineated more sharply. Concentrations of several amino acids were elevated by substituting crystalline amino acids for proteins, especially in postprandial plasma. Subjects responded differently to addition of the limiting amino acids, lysine and tryptophan, to the diets containing amino acids instead of rice plus wheat. Therefore, data obtained by means of combinations of cereals and by mixtures of their constituent amino acids cannot always be used interchangeably.
Six diets furnished 6.0 g of nitrogen to adult human subjects as follows: a combination of rice and wheat; mixtures in which either 100 or 50% of the amino acids in rice and wheat were replaced by their constituent amino acids; and similar diets in which lysine was increased from 1.2 to 1.8 g. Nitrogen retention was greater (P less than 0.01) and concentrations of several amino acids in plasma were lower when the cereals were supplemented with lysine than when all other diets were fed. Data obtained with mixtures of amino acids apparently cannot always be used interchangeably with that from cereal-based diets, even when amino acid content is the same. Changes in plasma amino acids are a useful indicator of utilization of dietary amono acids when nitrogen balance also is determined.
Opaque-2 corn, modified high-lysine corn with vitreous endosperm, and common corn were compared in rat growth studies. Corn alone supplied 8.6% protein; and at both 8.6 and 11.4% protein, corn furnished 60% of the protein and either milk or black beans supplied 40%. The modified corn, which also was high in both lysine and tryptophan, did not differ significantly from Opaque-2 corn in its ability to stimulate growth and nitrogen deposition in both well-nourished and partially protein-depleted rats; and both were significantly superior to common corn when fed alone. Milk was a more effective supplement for corn than black beans, especially when high-lysine varieties were fed, whereas beans exerted a similar effect on all varieties of corn. The depleted rats deposited more nitrogen as a result of eating most diets than did well nourished rats. Implications of these findings for preschool children are discussed.
In studies designed to evaluate the role of the liver and muscle in modifying the plasma amino acid response, three levels of dietary amino acids, 3.6%, 4.8% and 6.0% were fed to three groups of young adult male rats for 2 weeks. After fasting, either [U-14C]-L-leucine, [U-14C]-L-lysine or [U-14C]-L-alanine was administered intragastrically with a portion of diet. After a 4.5 hour fast, rats were killed. Distribution of radioactivity was evaluated in trichloroacetic acid (TCA) supernatants and lipid-extracted precipitates of plasma, liver and gastrocnemius muscle, and in expired CO2. Free amino acids were measured and specific activities of amino acids were determined. Rats fed 6.0% or 4.8% amino acids lost less weight than those fed 3.6%. A high percentage of radioactivity from 14C-leucine and 14C-lysine was recovered in the lipid-extracted precipitate. TCA supernatants from rats fed 14C-leucine contained low levels of radioactivity. A large percentage (60%) of the radioactivity from 14C-alanine was expired in 14CO2. The percentages of alanine found in TCA precipitates were very low. Significant increases in concentration associated with increments in dietary amino acids occurred in plasma free isoleucine, leucine, valine and tyrosine; liver free histidine; and muscle free leucine and threonine. Concentrations of many amino acids were depressed in the muscle of rats fed 4.8% amino acids whereas they increased in response to 6.0%. Protein and free amino acid specific activities indicated no change in rates of protein synthesis. Data from this type of experiment may assist in interpreting the role of the liver and muscle in modifying the plasma amino acid response to dietary amino acids.
Experimental diets that furnished approximately 6.0 g of nitrogen per day were consumed by young men. Nitrogen retention was not altered significantly when egg albumen was replaced by its constituent essential and nonessential amino acids or by the essential amino acids (including cystine, tyrosine and histidine) plus a source of nonspecific nitrogen. Concentrations of essential amino acids in fasting or postprandial plasma were not influenced significantly by source of amino acids or by replacement of nonessential amino acids by nonspecific nitrogen; but concentrations of certain nonessential amino acids were altered by treatment. Responses to an elemental diet or to a similar diet in which egg albumen replaced the amino acid mixture did not differ significantly.
Explore the source record for details and available documents.
Explore the source record for details and available documents.